The challenge while eating less overall is to eat more nutrient-rich foods, such as fruits, vegetables, whole grains, nuts, beans, fish, low-fat dairy products, and lean cuts of meat.

As you age, your body needs the same amount of protein, vitamins, and minerals and, in some instances, even more nutrients.

Take vitamin B-12, for example. After age 50, your body's ability to absorb the vitamin often fades because you don't have as much stomach acid, which is needed to break B-12 down from food sources.

The same holds true for vitamin D. Aging skin is less able than younger skin to change sunlight to the vitamin. That, in turn, affects the body's ability to absorb calcium.

You need both vitamin D and calcium to prevent bone loss. Ask your doctor if you are getting enough of those must-have nutrients, and if you aren't, what foods you should eat and whether you need a supplement. If your doctor isn't sure, ask for a referral to a dietitian.

Also, make sure you drink water. That's important at any age, but in your later years, you may be less likely to notice your thirst, Bales says.

Perhaps the biggest myth about nutrition and aging? That older people are set in their ways. "That really is not true," Bales says. "I've found that most are really motivated about their health, and many of them are quite willing to try to change."